This invention relates to industrial gas turbine technology and specifically, to a floating tip shroud configuration for a compressor stator.
Severe loading of cantilevered stator blades, caused by off-design operation, may result in incident angles and pressure gradients that cause damaging, unsteady aerodynamic forces. These aerodynamic forces have led, under certain conditions, to stator blade failure. In particular, the flow around a stator blade tip, from pressure to suction side, has been shown to create forces of sufficient magnitude and frequency to lead to failure of the blade.
This problem is amplified, for example, in the last stator stages of certain heavy-duty industrial turbines, due to tip clearance effects when the cantilevered stator is positioned between two static ring segments which undergo significant temperature variations. The outer ring (or outer carrier ring) is typically fixed to the compressor outer case while the inner ring (or tip shroud) is typically secured to the compressor inner barrel. During turbine startup, the gas path and stator blade temperatures increase rapidly, closely followed by the inner ring. The outer ring has a much slower thermal response due to its size and thermal boundaries. The cantilevered stator blades are attached via the outer ring, to the outer compressor case and therefore follow the outer case radial growth. Since it is undesirable to have any flexible, cantilevered blades contact the inner ring, a large clearance between the blade tips and the inner ring is required. The startup transient defines the required clearance to prevent contact. During steady state operation, the outer ring has warmed up and pulls the stator blades away from the inner ring, thereby increasing the tip clearance. Increased tip clearance has been shown to increase the unsteady aerodynamic loading.
One prior solution has been to weld tip shrouds on the blade tips. While this does eliminate the tip clearance issue, it creates a number of new cost and manufacturing challenges. There is a continuing need, therefore, for a much simpler and less expensive solution to the above problems.